1. Field
Exemplary embodiments of the present invention relate to a backlight unit that supplies light to a liquid crystal display panel of a liquid crystal display.
2. Discussion of the Background
A liquid crystal display (LCD) is a widely-used flat panel display. In general, in a display panel of the LCD, a liquid crystal material is filled between an upper substrate on which a common electrode and a color filter are formed, and a lower substrate on which a thin film transistor and a pixel electrode are formed. Different electrical potentials are applied to the pixel electrode and the common electrode to generate an electric field to change alignment of liquid crystal molecules in the liquid crystal material and, as a result, adjust light transmittance to display an image on the display panel.
Because a liquid crystal display panel of the LCD is a non-emissive light receiving device, a backlight unit is generally required in the LCD to provide light to the liquid crystal display panel from the lower part of the liquid crystal display panel.
In the backlight unit, a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is generally used as a light source. In the related art, the CCFL, which provides bright white light with low power consumption, is mainly used. However, an LED, which has advantages such as excellent color reproducibility, long life-span, and low power consumption as compared with the CCFL, is increasingly being used.
The backlight unit is classified into an edge-type and a direct-type in accordance with a position of the light source with respect to the liquid crystal display panel. In the edge-type, a light source is disposed at a side of the liquid crystal display panel to provide light through a light guide at the side. In the direct-type, the light source is disposed at a rear side of the liquid crystal display panel to provide light to the liquid crystal display panel. Between the edge-type and the direct-type, the direct-type backlight unit has advantages of high light utilization coefficient, simple treatment, no limitation of size of the display panel, and relatively low cost.
When the LED, which is a point light source, is used as a light source of the direct-type backlight unit, an optical lens is provided above the light emitting surface of an LED package to refract the LED light. This is done to prevent concentration of LED light, which travels in a straight line, above a light-emitting surface and, instead, to distribute LED light over the entire liquid crystal display panel. Generally, a diffuser sheet and a prism sheet are disposed above the optical lens. The diffuser sheet changes light passing through the optical lens into a surface light source having a uniform brightness, and the prism sheet changes side light into front light and focuses radiating light.
In order to improve optical efficiency of the liquid crystal display, a reflective polarization sheet (also referred to as a “reflective polarization film”), which converts a light component to be absorbed by a polarizer of the liquid crystal display panel into light which is to be transmitted by the polarizer, may be disposed on an upper surface of the backlight unit.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not constitute the prior art.